The invention relates to bacterial plasmids.
Plasmids are small, extra-chromosomal, mostly circular and independently replicating DNA molecules, which occur in nearly all bacteria and also in some eukaryons as well as in the mitochondria. The size of the plasmids vary between approximately 1.5 to 300 kb.
As a rule bacterial plasmids are circular, covalently closed and supercoiled. They often carry resistance genes against antibiotics or heavy metals, genes for the metabolization of a typical substrates or genes for a number of specie-specific characteristics, such as metabolic properties or virulence factors. Some plasmids can be transferred from one cell into another. Because the pathogenity of bacteria is determined according to present views, partly also by the properties of the plasmids, there exists increasingly a greater interest to clarify the properties of the plasmid DNA.
It is known of the family of entereobacteriacea, to whom 14 main varieties and 6 further varieties belong, that family members can develop different properties. Typical family members are, for example, Escherichia, Salmonella and Klebsiella. Escherichia coli (E. coli) is the classic model for the study of bacterial genetics. By discovering and characterizing different virulence factors of E. coli, strains of this species were generally found to exhibit differences in human and animal pathogenicities. These differences may be extreme, ranging from avirulence to high grade virulence, such as in the case of the recently spreading variant known as xe2x80x9cEHECxe2x80x9d. Thus, a number of virulence factors have been described for extra-intestinal as well as for intestinal E. coli strains, which have been partially characterized. The sero-variety 06:K5 virulence factors, such, as for example, haemolycin and P-fimbrial adhesion are known to be associated with pathogenic E. coli, while apathogenic representations of this sero-variety typically lack these virulence factors.
As in rule virulence genes are found at enterobacteria on large plasmids (approximately 60 kb). There are also enterobacteria with small, so-called cryptic plasmids, whose function hitherto could not be reliably determined.
Because it is known that E. coli virulence factors are at least partly also present in genes of the plasmids, there exists a need for further, data regarding the detection and characterization of plasmids in enterobacteria, especially Escherichia. Such information will improve, for example, diagnostic and therapeutic treatment of enterobacterial infections. Such plasmids, or their bacterial carriers, or corresponding synthethized DNA can be applied medicinally in therapeutics or for prophylaxis of Enterobacterial infections, as well as for nutritional, physiological or probiotic purposes in microbiological analysis or diagnostics testing of such infections. Furthermore, plasmids, especially those of E. coli, are known expression vectors used in genetic engineering, increasing the interest in and learning more about the properties of such plasmids.